Noble metals have long been the standard in localized surface plasmon resonance (LSPR) research and are used in applications such as surface enhanced Raman scattering, photocatalysis, and refractometric sensing. However, there is growing interest in plasmonic semiconductor nanomaterials where substitutional and vacancy doping can be utilized to directly modify the optoelectronic properties of the observed LSPR. According to the simplified Drude model, the LSPR frequency is governed by both the free carrier density (n) and effective mass (m*) of these carriers. m* has often been neglected in previous literature, with the assumption that it remains constant relative to carrier density changes. However, in order to accurately extract information using the Drude model, it is necessary to challenge this assumption. For this experiment, CuxFeS4 (x=7,5,3) nanocrystals (NCs) are selected due to their near-infrared LSPR at 1100 nm. With low elemental cost, high biodegradability, and a biologically transmissive plasmon frequency in mind, CuxFeS4 is an ideal candidate for applications such as in-vivo plasmon enhanced luminescence and infrared neural stimulation. Adjusting the Cu:Fe ratio should lead to changes in the defect density and structural composition of the NCs, but the observed LSPR does not significantly change in either frequency or intensity. To understand how the free carriers within the NC are changing in such a way to produce near identical LSPR extinction features, a full picture of m* and n is required. High field magnetic circular dichroism (MCD) allows for the direct measurement of m* by inducing cyclotron resonance via an applied magnetic field. Experimentally obtained spectra are subsequently fit using a least-squares method in order to generate a simulated MCD spectrum for analysis. CuxFeS4 is confirmed to be a p-type semiconductor and the m* values for each ratio are measured and quantified.

Investigation of the Cu:Fe ratio on effective carrier mass for CuxFeS4 through high field magnetic circular dichroism

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.